Portable telephone units, personal computers and the like electronic devices are getting smaller in size and lighter in weight. Among them, an increasing number of recent models have been designed into a so-called foldable body structure, where a body is formed of a fixed cabinet and a movable cabinet which are coupled together like a clam shell. It is requested that the body can be opened and closed comfortably with high reliability.
A conventional opening and closing device used for the above purpose is described with reference to FIG. 5 through 7. Among the drawings, cross sectional views are illustrated magnified in the radius direction in order to show the inter-relationship of fixed cam and movable cam clearly.
FIG. 5 is a cross sectional view showing a conventional opening and closing device, FIG. 6 shows the exploded perspective view. Referring to FIG. 5 and FIG. 6; opening and closing device 10 includes fixed member 1, fixed cam 2, movable member 3, movable cam 4, case 5, spring 6, fixed shaft 7 and end ring 8. Fixed member 1 is made with a metal material; it has a substantially round cylindrical shape and provided at the left side with fixing portion 1A. Fixed cam 2 is provided at the right of fixed member 1 along the outer circumference; it is formed of protruding portion 2A and two slopes 2B and 2C stretching in the right and the left directions from protruding portion 2A.
Movable member 3 is made with a metal material; it has a substantially round cylindrical shape like fixed member 1. Movable cam 4 is provided at the left of movable member 3, or at the side opposing to fixed cam 2, along the outer circumference. Movable cam 4 is disposed so that it can rotate with respect to fixed member 1 in the direction of open and close. Case 5 is made with a sintered alloy metal, shaped into a substantially round cylindrical form. Case 5 is provided with guide groove 5A which is protruding outward. Guide groove 5A allows insertion of guide protrusion 3A, which is protruding from the outer circumferential surface of movable member 3, for supporting movable member 3 so that it can move along the direction of axis within case 5. In this way, a guiding mechanism is provided.
Spring 6, which has a coiled shape, is mounted in a slightly compressed state in case 5 between the right side of movable member 3 and case 5's right end-bottom. Spring 6 pushes movable member 3 to the left so that the tip end of movable cam 4 makes an elastic contact with fixed cam 2 at slope 2B. Fixed shaft 7 has a substantially round column shape. The left end of fixed shaft 7 is connected tight with fixed member 1, while the right end goes through movable member 3's central void and spring 6 to be supported by means of end ring 8 so as it can rotate with respect to the right end of case 5. Fixed member 1's fixing portion 1A is pushing out of the left side of case 5, and allowed to rotate. Case 5 houses fixed member 1, movable member 3, spring 6 and other items.
FIG. 4A through 4D are perspective views of a portable telephone unit, which incorporates an opening and closing device. The above-configured opening and closing device 10 is mounted in a portable telephone unit to couple fixed cabinet 22 and movable cabinet 23 together as shown in FIG. 4B, a perspective view. Describing more practically; fixing portion 1A of fixed member 1 is connected tight with fixed cabinet 22 which houses operating portion 22A consisting of a plurality of keys disposed on the surface area and sound input portion 22B consisting of a microphone, etc., while the outer circumferential surface of case 5's guide groove 5A is connected tight with movable cabinet 23 which includes display portion 23A such as a liquid crystal display (LCD) disposed on the surface area and sound output portion 23B consisting of a speaker, etc. Thus, fixed cabinet 22 and movable cabinet 23 are pivotally supported to be foldable by means of opening and closing device 10 to constitute the body of a portable telephone unit, or an electronic apparatus.
FIG. 7A through 7D are cross sectional views in part of a conventional opening and closing device. In a state where the tip end of movable cam 4 of conventional opening and closing device 10 is making an elastic contact with fixed cam 2 at lower slope 2B, as illustrated in FIG. 5, movable member 3 is pressed downward, or towards the direction of closing, by the force of spring 6. Under this state, since the right end of guide protrusion 3A is having an elastic contact with guide groove 5A at the right as illustrated in FIG. 7A, movable cabinet 23 connected tight with case 5 is held at the closed stance with respect to fixed cabinet 22, as shown in FIG. 4A.
When movable cabinet 23 is opened by the hand as shown in FIG. 4B, the motion is conveyed via case 5 which is connected tight with movable cabinet 23, causing movable member 3 to rotate and move along the axis direction within case 5. The tip end of movable cam 4 travels beyond fixed cam 2's protruding portion 2A, as shown in FIG. 7B, to make an elastic contact with left slope 2C. Then, movable member 3 is provided with a force towards the left, or an opening force, and the left end of lowered guide protrusion 3A makes an elastic contact with guide groove 5A at the left. As the result, movable cabinet 23 is provided with an opening force.
The tip end of movable cam 4 further slides along slope 2C keeping an elastic contact, and the left end of lowered guide protrusion 3A pushes guide groove 5A at the left, as illustrated in FIG. 7C, and then case 5 rotates towards the opening direction. When the tip end of movable cam 4 arrives at a certain specified location, movable cabinet 23 is brought to a certain predetermined open angle of about 150–170 degrees with respect to fixed cabinet 22, as shown in FIG. 4C.
As described in the above, opening and closing device 10 works in such a way that the rotating motion of case 5, which is connected tight with movable cabinet 23, causes movable member 3 to move in the axis direction, and the tip end of movable cam 4 is made to have an elastic contact with either one of slopes 2B and 2C of fixed cam 2. Under the operation of the above-described mechanism, movable cabinet 23 opens and closes relative to fixed cabinet 22.
If movable cabinet 23, which has already been opened to a certain predetermined angle, is hit by an external power and forced to open further beyond the angle, for example if it is pushed by mistake from the behind as illustrated in FIG. 4D, conventional opening and closing device 10 allows case 5 to make an additional revolution for a small amount identical to the small gap existing between guide groove 5A and guide protrusion 3A as shown in FIG. 7D. However, it is not allowed to make any further opening action after the right face of guide protrusion 3A got in touch with guide groove 5A at the right and movable cam 4 touched the next fixed cam 2. The structure of such a conventional opening and closing device has been disclosed in, for example, Japanese Patent Unexamined Publication No. 2004-245342.
In the above-described conventional opening and closing device, an issue how to prevent a possible damage that could be incurred on fixed cam 2 and/or movable cam 4 when an external power is incidentally given to an already-opened body forcing it to open further is remaining as an outstanding problem to be solved. If a countermeasure is to be built in a hinge, the cam size had to be made larger, a separate stopper mechanism had to be prepared for fixed cabinet 22 and movable cabinet 23, or the like extra means had to be contrived. In any way, a hinge after countermeasure inevitably grew bigger in the overall size and/or more complicated in the total mechanism.